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The phase characteristics of gyrotron traveling-wave tubes (gyro-TWTs) for high-resolution imaging radars have been investigated. Determinant equations of output phase are classified into the cold phase and warm phase in the cases of cold-field and hot-field regions, respectively. The phase–frequency characteristics of cold phase are examined regarding single-mode and multimode operations, respectively. The time stability and the sensitivity to external parameters of warm phase are also investigated. The efficient methods to make the output phase of gyro-TWTs controllable are proposed. The measured output phase of the input coupler and output taper of a Ka-band gyro-TWT is linear with respect to the frequency, without any distortion. Moreover, the warm output phase fluctuation introduced by the RF circuit is less than ±8°. [ABSTRACT FROM AUTHOR]

Novel compact input and output couplers for broadband operation of sheet beam traveling wave tubes are analyzed, designed, and cold tested. Multistage stepped waveguide and cascaded Bragg resonators are proposed and applied to improve the performance and extend the operating bandwidth. Optimized curve-Bragg resonators are studied to correct the phase between the reflector and $H$ -bend waveguide, which bring about a further enhancement of the coupler behavior. HFSS simulations predict a −3 dB transmission bandwidth about 38% and 34% are achieved, respectively, in Ku and $Q$ band. Besides, the large beam tunnel property of this kind of coupler benefit the beam transport of sheet beam devices. Different components as the input and output couplers for Ku- and $Q$ -band SB-TWT are manufactured and cold tested. Results of vector network analyzer measurement and simulation present an excellent agreement. [ABSTRACT FROM AUTHOR]